Longitudinal Trajectories of Brain Volume and Cortical Thickness in Treated and Untreated Primary Human Immunodeficiency Virus Infection

HIV infection and cerebral small vessel disease are independently associated with brain atrophy and cognitive impairment

OBJECTIVE

The objective of this study is to investigate whether cerebral small vessel disease (CSVD) is more common in virologically suppressed HIV-positive participants compared with HIV-negative controls and examine the potential synergistic effects of HIV and CSVD on brain structure and cognition.

DESIGN

Cross-sectional analysis of 119 treated, virologically suppressed HIV-positive and 55 HIV-negative participants. Forty-six HIV-positive and 30 HIV-negative participants had follow-up 2 years later. All participants underwent MRI and neuropsychological testing.

METHODS

Volume of white matter hyperintensities (WMH) was used as a surrogate measure of CSVD severity. Tensor-based morphometry and cortical modeling estimated brain volumes and cortical thickness, respectively. Rasch measurement theory was applied to neuropsychological test scores to estimate overall cognition. Linear models compared WMH loads, brain volumes, and cognition between groups; evaluated the association of WMH loads with brain volumes and cognition; and tested the interaction between HIV and WMH loads on brain volumes and cognition. Mixed-effects models compared the change in WMH loads between groups.

RESULTS

WMH loads and change in WMH loads were similar between the groups. HIV-positive participants had poorer cognition, thinner cortex and reduced subcortical volumes compared with HIV-negative controls. Higher WMH loads were associated with reduced cortical thickness and subcortical volumes and worse cognition, regardless of HIV serostatus. No significant interactions were observed between HIV and WMH loads with regards to brain volumes or cognition.

CONCLUSION

These findings suggest that the contributions of HIV and CSVD on brain atrophy and cognitive impairment are independent but additive processes. This argues that optimizing vascular health may mitigate brain injury and cognitive decline, especially in treated, virologically suppressed HIV-positive individuals.

Neurocognitive Phenotyping of HIV in the Era of Antiretroviral Therapy

PURPOSE OF REVIEW

This paper examines the theoretical and empirical basis for neurocognitive phenotyping of HIV.

RECENT FINDINGS

The pattern of neurocognitive symptoms associated with HIV has traditionally been referred to as a "subcortical" phenotype. Recent concern has been raised that the neurocognitive phenotype in the post-ART era has changed to reflect the addition of cortical features, suggestive of synergistic age-related neurodegeneration. Empirical evidence reviewed in this paper suggests that, when present, HIV-related neurocognitive impairment in the post-ART era remains subcortical in nature, regardless of advanced age or treatment status. Persistent neurocognitive impairment among virally suppressed individuals may reflect a combination of HIV disease factors, pre-existing risk factors, and/or emergent health comorbidities such as subcortical ischemic vascular disease in older people living with HIV. An entrenchment of the subcortical neurocognitive phenotype of HIV appears to be unfolding in the post-ART era. Whether new neurocognitive subtypes of HIV exist in the current era requires additional research utilizing harmonized test protocols and advanced computational methods capable of deep phenotyping. Recommendations from other neurological disorders are provided.

Visual evoked and event-related brain potentials in HIV-infected adults: a longitudinal study over 2.5 years

PURPOSE

The aim of this neurophysiological study was to monitor changes in the visual and cognitive function of HIV-infected patients treated with combination antiretroviral therapy.

METHODS

Eleven adult Czech HIV+ patients, with a mean age of 35 years and CD4 cell count ≥ 230 × 10⁶ cells/L of blood at the time of enrollment, underwent four to six examinations over the course of 2.5 years to evaluate pattern-reversal and motion-onset visual evoked potentials (P-VEPs and M-VEPs), visually driven oddball event-related potentials (ERPs) and Montreal Cognitive Assessments. In addition to evaluating the intraindividual change in the observed parameters, we also compared patient data to data from eleven age- and gender-matched controls.

RESULTS

We did not find any significant differences in P-VEPs between the patients and controls or in the paired comparison of the first and last visit. The only significant finding for P-VEPs was a linear trend in prolongation of the 20' P-VEP P100 peak time. In M-VEPs, we found a significant intergroup difference in the N160 peak time recorded during the first visit for peripheral M-VEPs only. During the last visit, all N160 peak times for patients differed significantly from those of the control group. The only intervisit difference close to the level of significance was for peripheral M-VEPs, which confirmed the trend analysis. No significant differences between patients and controls were found in the ERPs, but the P300 peak time showed a significant difference between the first and last visits, as confirmed by the trend. Patient reaction time was not significantly delayed at the first visit; however, it was prolonged with time, as confirmed by the trend.

CONCLUSION

Our aim was to evaluate whether antiretroviral treatment in HIV+ patients is sufficient to preserve brain visual function. The optic nerve and primary visual cortex function tested by the P-VEPs seem to be preserved. The prolongation of the M-VEPs suggests an individually detectable decline in CNS function, but these changes did not show a progression during the follow-up. From a longitudinal perspective, the trends in peak time prolongation of the 20' P-VEP, peripheral M-VEP, ERP and reaction time suggest a faster decline than that caused by aging in healthy populations, as previously described in a cross-sectional study.

Different roles of frontal versus striatal atrophy in HIV-associated neurocognitive disorders

Gray matter (GM) atrophy is frequently detected in persons living with HIV, even in the era of combination antiretroviral therapy (cART), but the specificity of regions affected remains elusive. For instance, which regions are consistently affected in HIV? In addition, atrophy at which regions is frequently associated with neurocognitive impairment in HIV? Resolving these questions can potentially help to establish the possible neural profiles of HIV-associated neurocognitive disorders (HAND) severity, which currently is solely defined by neurobehavioral assessments. Here, we addressed these questions using a novel meta-analysis technique, the colocalization-likelihood estimation (CLE) technique, to quantitatively synthesize the findings of GM atrophy in HIV+ adults. Twenty-one of 386 studies published between 1988 and November 2017 and identified in PubMed were selected, plus four identified in other resources. In the end, 25 studies (1,370 HIV+ adults, 889 HIV- controls) were included in the meta-analysis. This technique revealed that GM atrophy in HIV+ adults was dominated by two distinct but nonexclusive profiles: frontal (including anterior cingulate cortex, [ACC]) atrophy, which was associated withHIV-disease and consistently differentiated HIV+ adults from HIV- controls; and caudate/striatum atrophy, which was associated with neurocognitive impairment. The critical role of caudate/striatum atrophy in neurocognitive impairment was further supported by a separate data analysis, which examined the findings of correlation analyses between GM and neurocognitive performance. These results suggest that the frontal lobe and the striatum play critical but differential roles in HAND. A neural model of HAND severity was proposed with several testable predictions.

Molecular Imaging of Neuroinflammation in HIV

The development of combined antiretroviral therapy (cART) has increased the lifespan of persons living with HIV (PLWH), with most PLWH having a normal life expectancy. While significant progress has occurred, PLWH continue to have multiple health complications, including HIV associated neurocognitive disorders (HAND). While the exact cause of HAND is not known, persistent neuroinflammation is hypothesized to be an important potential contributor. Molecular imaging using positron emission tomography (PET) can non-invasively evaluate neuroinflammation. PET radiotracers specific for increased expression of the translocator protein18kDa (TSPO) on activated microglia can detect the presence of neuroinflammation in PLWH. However, results from these studies have been inconsistent and inconclusive. Future studies are needed to address key limitations that continue to persist with these techniques before accurate conclusions can be drawn regarding the role of persistent neuroinflammation in PLWH.

Effects of HIV Infection, methamphetamine dependence and age on cortical thickness, area and volume

OBJECTIVE

This study examined the effects of HIV infection, methamphetamine dependence and their interaction on cortical thickness, area and volume, as well as the potential interactive effects on cortical morphometry of HIV and methamphetamine with age.

METHOD

T1-weighted structural images were obtained on a 3.0T General Electric MR750 scanner. Freesurfer v5.3.0 was used to derive cortical thickness, area and volume measures in thirty-four regions based on Desikan-Killiany atlas labels.

RESULTS

Following correction for multiple statistical tests, HIV diagnosis was not significantly related to cortical thickness or area in any ROI, although smaller global cortical area and volume were seen in those with lower nadir CD4 count. HIV diagnosis, nevertheless, was associated with smaller mean cortical volumes in rostral middle frontal gyrus and in the inferior and superior parietal lobes. Methamphetamine dependence was significantly associated with thinner cortex especially in posterior cingulate gyrus, but was not associated with cortical area or volume following correction for multiple statistical tests. We found little evidence that methamphetamine dependence moderated differences in cortical area, volume or thickness for any ROI in the HIV seropositive group. Interactions with age revealed that HIV diagnosis attenuated the degree of age-related cortical thinning seen in non-infected individuals; intercepts indicated that young HIV seropositive individuals had thinner cortex than non-infected peers.

CONCLUSIONS

Methamphetamine dependence does not appear to potentiate a reduction of cortical area, volume or thickness in HIV seropositive individuals. The finding of thinner cortex in young HIV seropositive individuals and the association between CD4 nadir and global cortical area and volume argue for prioritizing early antiretroviral treatment.

Chronic Viral Neuroinflammation: Speculation on Underlying Mechanisms

Viral infection in the brain can be acute or chronic, with the responses often producing foci of increasingly cytotoxic inflammation. This can lead to effects beyond the central nervous system (CNS). To stimulate discussion, this commentary addresses four questions: What drives the development of human immunodeficiency virus (HIV)-associated neurocognitive disorders, does the phenotype of macrophages in the CNS spur development of HIV encephalitis (HIVE), does continual activation of astrocytes drive the development of HIV-associated neurocognitive disorders/subclinical disease, and neuroinflammation: friend or foe? A unifying theory that connects each question is the issue of continued activation of glial cells, even in the apparent absence of simian immunodeficiency virus/HIV in the CNS. As the CNS innate immune system is distinct from the rest of the body, it is likely there could be a number of activation profiles not observed elsewhere.

Distinguishing Brain Impact of Aging and HIV Severity in Chronic HIV Using Multiparametric MR Imaging and MR Spectroscopy

Background

Combination antiretroviral therapy (cART) has transformed HIV into a manageable but complex chronic disease, in which it is uncertain which brain insults may relate to age vs initial disease severity. We evaluate N-acetyl-aspartate/creatine (NAA/Cr), white matter hyperintensities (WMH), and mean cortical thickness to identify which subclinical markers of brain insult best relate to CD4 nadir and aging. This is a prospective study of the association between brain markers with age and initial infection severity, based on CD4 nadir, in chronic HIV patients.

Methods

Thirty-seven chronic HIV patients (age 25–77 years) with successful viral suppression were scanned on a GE 3T magnetic resonance imaging scanner to obtain NAA/Cr (standardized and averaged over 5 brain regions), log-transformed WMH volume, and mean cortical thickness. The brain measures were fitted with both CD4 nadir and age to evaluate the significance of their relationship.

Results

NAA/Cr, WMH, and cortical thickness were all correlated with age and CD4 nadir in unadjusted associations. Stepwise regression models showed that NAA/Cr alone best predicted CD4 nadir (β = 40.1 ± 13.3; P = .005), whereas WMH (β = 2.3 ± .9; P = .02) and mean cortical thickness (β = –2.7 ± 6.6; P < .0001) together produced the best model fit with age. NAA/Cr was higher for HIV stage 1 (CD4 nadir ≥ 500 cells/ µL; n = 15) compared with stage 2 (200 ≥ CD4 nadir < 500; n = 13) and stage 3 (CD4 nadir < 200; n = 9; P < .01 for both).

Conclusions

In patients with effectively suppressed HIV, NAA reflects the subclinical brain impact of initial disease severity related to development of even mild immune compromise, whereas cortical thickness and WMH volume are useful to evaluate age-related changes.

The Impact of Alcohol Use on Frontal White Matter in HIV

BACKGROUND

Alcohol use disorder (AUD) is prevalent among individuals diagnosed with human immunodeficiency virus (HIV), and both HIV and alcohol use have been shown to negatively affect the integrity of white matter pathways in the brain. Behavioral, functional, and anatomical impairments have been linked independently to HIV and alcohol use, and these impairments have bases in specific frontally mediated pathways within the brain.

METHODS

Magnetic resonance imaging data were acquired for 37 HIV+ participants without dementia or hepatitis C. Imaging data were processed through the FreeSurfer and TraCULA pipelines to obtain 4 bilateral frontal white matter tracts for each participant. Diffusion metrics of white matter integrity along the highest probability pathway for each tract were analyzed with respect to demographics, disease-specific variables, and reported substance use.

RESULTS

Significantly increased axial diffusivity (decreased axonal integrity) and a trending increase in mean diffusivity were observed along the anterior thalamic radiation (ATR) in participants with a history of AUD. A diagnosis of AUD explained over 36% of the variance in diffusivity along the ATR overall when accounting for clinical variables including nadir CD4 and age-adjusted HIV infection length.

CONCLUSIONS

This study provides evidence of HIV-related associations between alcohol use and indicators of axonal integrity loss along the ATR, a frontal pathway involved in the inhibition of addictive or unwanted behaviors. Reduced axonal integrity of this pathway was greatest in HIV+ participants with an AUD, even when considering the effect of age-adjusted disease length and severity (nadir CD4). This finding implicates a potential biological mechanism linking reduced integrity of frontal white matter to the high prevalence of AUD in an HIV+ population without dementia or hepatitis C.